1. Field of the Invention
The present invention relates to a device for controlling a feeding of a continuous form in a printer in which printing of the continuous form is carried out by an electrophotographing process.
2. Description of the Related Art
For printing data output from a computer, a dot impact type line printer, which uses a continuous form and starts the printing process after accumulating printing data corresponding to one line of printing, is generally used.
The continuous form is a fan-fold paper form which is foldable and is provided with sprocket holes, and is constructed in such a manner that the folding portions thereof correspond to perforations by which the continuous form is easily separated into individual pages. The printer is usually constructed such that the printing process is carried out in such a manner that the space on each side of the perforations is not printed, and thus printed data is not split when the continuous form is separated into individual pages.
Recently, due to improvements in the printing speed thereof, a printer printing a continuous form by an electrophotographing process has been proposed.
In the electrophotographing process, exposure to a sensitive drum, development and transfer to paper of the exposed image, and fixing of the transferred image by a heat roller are carried out in sequence to print an image on the form. This method is generally used in a copy machine.
Note that, when this electrophotographing process is applied to a printer, since the position on the sensitive drum at which an exposure is carried out and the position on the sensitive drum at which the printed image is transferred to the form are different from each other, the printer is constructed not as a line printer but as a page printer, which starts the printing process after printing data corresponding to one page of printing has been accumulated.
Further, a transferred printed image is usually fixed by thermofixing by heat rollers, and in this case, the position at which the fixing is carried out and the position at which a transfer is carried out cannot be the same, and therefore, a space must exist between the transfer position and the fixing position, which causes the following problem.
That is, in a printer in which each page is printed individually, since a printing of only one sheet of a form must be considered, the space referred to above (between transfer and fix positions) is not a problem. When a continuous form is used, however, if all of the transferred pages are fixed, a part of the form corresponding to the above space becomes useless. Therefore, a problem arises of what part of the transferred form should be fixed.
Further, taking into consideration the printing performance of the printer, an interruption and a restart of the transfer and fixing process are preferably carried out at the perforated portion of the continuous form, on which printed letters are not formed, and accordingly, the printer is preferably controlled in such a manner that a space between the transfer position and the fixing position corresponds to one page of the continuous form, and when the printing is stopped, a perforated portion thereof, which is a boundary between two adjacent pages, is at the transfer position or the fixing position.
In such a construction, however, when one printing process is finished and the next printing process awaited, one page of the continuous form, which has not been fixed, remains between the transfer position and the fixing position. Therefore, when printing data corresponding to the next one page is transferred, a fixing process is carried out for that page, which is then discharged from the printer. Therefore, in such a construction, the waste of a form due to the carrying out of a fixing at every transfer process is avoided.
In the case in which the end of the continuous form is reached, however, even if the last page is fixed, since it is the last page, the useless page of the continuous form as described above does not exist. Further, since the sprocket holes are engaged with projections of the tractor unit of the printer when a new continuous form is set therein, if the last page remains in the printer, the new continuous form cannot be installed the printer.